An uplink multiple-input multiple-output (Multiple-Input Multiple-Output, MIMO) technology and an uplink orthogonal frequency division multiple access (Orthogonal Frequency Division Multiple Access, OFDMA) technology have been widely applied to wireless communication, and are used as key technologies for improving a capacity and a user quantity. When the technologies are applied to the 802.11 family of standards, an access point (Access Point, AP) needs to send a trigger frame (Trigger Frame) to instruct receiving stations (Station, STA) to synchronously send uplink data frames of the receiving stations after a particular time.
According to the 802.11 standards, the particular time described above is generally defined as a short interframe space (Short Interframe Space, SIFS). Within the SIFS, a receiving station needs to first parse trigger information carried in the trigger frame, and then transmits data based on the trigger information by using an uplink transmission resource. However, the receiving station cannot complete the foregoing steps within the SIFS time.
Some solutions are proposed to resolve the problem. One solution is to extend the SIFS time, so that the time is enough for the receiving station to complete the foregoing procedures. However, in the method, a wait time between adjacent frames is increased, and therefore there is a hidden transmission conflict risk. Another solution is that the information carried in the trigger frame is placed in physical layer signaling (PHY Signaling) for transmission, so that processing of the information by a receive end can be accelerated, and it is ensured that the receive end can complete processing within the SIFS time. However, the method requires that the receiving station has a special receiving state machine for the signaling, and consequently complexity of a receiver is increased. In addition, because of a limit of a quantity of bits, the physical layer signaling may not be enough to accommodate an information amount in this scale.
A more acceptable solution is a padding (padding) design at a media access control (Media Access Control, MAC) layer. That is, unwanted signals are added after wanted signaling. The unwanted signals are a packet extension field in a MAC frame structure. The AP sends the unwanted signals, so that the receiving station has enough time to parse the trigger information carried in the trigger frame and then transmit the data based on the trigger information by using the uplink transmission resource, and it is ensured that the wait time between the adjacent frames is still the SIFS. However, the design is applicable to only a physical layer protocol data unit (physical layer protocol data unit, PPDU) of a legacy (legacy) type, but is not applicable to a later version.